The scenario that we have within my current organisation is that we have three related companies sharing a single office space. Two of the companies are using separate MS Exchange 2007 on premise environments, the third is using Microsoft Online.
We are looking for a solution whereby anyone from each of the three companies can 'book' meeting rooms from within Outlook/on their smartphones, and for all parties to have free/busy information.
There are many limitations handed down from HQ which affect our ability to form Active Directory domain trusts etc, so we have been tasked to find a way to achieve the intended objective without that.
All advice appreciated.